Many industrialized countries generate a substantial amount of their electricity in large centralized power plants and delivered via power lines on the utility power grid, or utility grid. Power plants are typically fossil fuel based, nuclear or hydroelectric. However, power may be generated locally, for example using local generators, and available solar, wind, or geothermal resources. The locally generated power is typically on its own grid, called a microgrid. Excess power generated on the microgrid can be sold back to the utility by tying the microgrid electrically into the local utility grid and net metering to determine the net flow of electricity into or out of the microgrid.
Traditionally, the utility grid is AC, or alternating current, and a microgrid interfaces to the utility grid using a grid-tie inverter. The grid-tie inverter uses anti-islanding switches that guarantees that the inverter is disconnected from the utility grid if power from the utility is down and only reconnects when utility is operating normally again. The anti-islanding switches are a safety feature that prevents the microgrid from supplying power onto the utility grid when utility workers may be repairing a downed power line or malfunctioning transformer. Although this protects the utility grids from power generated on the microgrid, there remains the possibility of power interruptions on the microgrid itself
A microgrid can participate in load-shedding programs with the utilities who then treat the microgrids as dispatchable loads that can be shed by the utility if needed. Owners of microgrids agree to be curtailed up to an agreed number of times and durations. In return, the incentive for the microgrid owner is usually a reduced energy rate that lowers the overall energy bill, or a capacity and/or energy payment for the actual load being placed at risk of interruption. Usually owners are notified when utility service is going to be interrupted and the verification that the customer load was shed as requested takes place ex post based on meter data. The owner can choose not to comply with the direction to shed load as requested, although penalties are often levied for non-compliance and may be severe. In some load-curtailment programs, loads are interrupted immediately and without warning. The present microgrid solutions do not address solutions for enabling loads to continue to be powered while complying with utility load-shedding requests.
As microgrids become more common, their influence on the stability of the grid will increase. Undesirable dynamic interactions triggered by microgrids increase the possibility of key, heavily loaded transmission lines tripping. The present microgrid solutions do not address designs of utility grids that utilize the dynamic nature of microgrids to enhance the stability of the utility grids and the transmission lines.